Because organic semiconductor materials have semiconducting and optoelectronic properties, they can be applied in many optoelectronic devices such as organic thin-film transistors (OTFT), organic solar cells, organic light-emitting diodes (OLED), and photo sensors. The organic semiconductor materials are utilized to form an active film on optoelectronic devices by solution coating. Optoelectronic devices utilizing organic semiconductor materials have advantages such as being lightweight, inexpensive, easy to fabricate, and flexible, in addition to their suitability for large-area fabrication. Conjugated polymers with a conjugated backbone are among the most popular organic semiconductor materials for use in optoelectronic devices. However, the conjugated polymer has disadvantages, such as low carrier mobility and a narrow absorption band of about 400 nm to 650 nm. As such, the application of conjugated polymers in optoelectronic devices is limited. Therefore, many conjugated polymers are synthesized to enhance carrier mobility and the absorption band thereof, to further improve photoelectric efficiency.
In solar cell applications, characteristics such as high electron/hole mobility and a wide absorption band are desirable for improving power-conversion efficiency. Photo-induced or electro-induced charges are easily recombined to dissipate in an improper active layer, thereby lowering the power-conversion efficiency of an organic solar cell, including the improper active layer. If the solar light absorption is increased and the carrier mobility is enhanced, the power-conversion efficiency of the organic solar cell can be greatly increased. Thus, an electron donor material such as polymer is often combined with an electron acceptor material such as C60 by heterojunction technology. For example, the electron donor material poly(3-hexylthiophene) (P3HT) blended with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) has a power-conversion efficiency of 3.5%.
Therefore, a novel p-type organic semiconductor material for replacing the P3HT to improve the organic solar cell performance (e.g. power-conversion efficiency) is still called-for.